Deterioration of material from corrosion remains a challenging problem across many industries. It is expected that the annual losses due to corrosion of materials in the United States alone is about US$350 billion, or 3-4% of the gross domestic product. Accordingly, a vast industry has emerged around the development of corrosion protection coatings and the like.
However, developing successful coatings that provide corrosion protection of metals and alloys is a challenging task, partly due to restrictions imposed by the Environmental Protection Agency (EPA) on the use of environmentally hostile chemicals. For example, aluminum and its alloys have historically been protected by thin chromate conversion coatings or chromated primers, but the EPA has placed restrictions on the use of these coatings and primers due to the health risks associated therewith.
Unfortunately, alternatives to chromate conversion coatings also face their own set of problems. Organic-inorganic, ceramic-polymer hybrid (i.e., ceramer) materials possess excellent environmental stability, but their long-term use in aggressive climates remains questionable. Free volume associated with these hybrid coatings often provides percolation pathways for ions and electrolytes to reach the substrate material and initiate corrosion. Many organic coatings are susceptible to in-diffusion of moisture due to their micro-porous structure, and also tend to degrade in the presence of solar radiation. Inorganic coatings may be relatively impervious and resistant to solar degradation, but tend to be brittle and susceptible to cracking on flexible substrates. Silicone-based coatings can include relatively high hydrocarbon content to ensure good adhesion to the substrate, but tend to fail due to moisture-induced delamination. Even the material on which a corrosion protection coating is to be used can lead poor performance. For example, the adherence of corrosion protections coatings to aluminum materials can be hindered by the rapid formation of an inert oxide layer on the top of bare aluminum surfaces.